Ceiling construction



June 15, 1965 H. ZNAMIROWSKI EI'AL 3,189,139

CEILING CONSTRUCTION Filed June 26, 1962 4 Sheets-Sheet 1 June 15, 1965 H. ZNAMIROWSKI ETAL 3,189,139

CEILING CONSTRUCTION 4 Sheets-Sheet 2 Filed June 26, 1962 FIG. I4

FIG. lA

June 15, 1965 H. ZNAMIROWSKI ETAL 3,189,139

CEILING CONSTRUCTION 4 Sheets-Sheet 3 Filed June 26, 1962 FIG. 7

lilnllllllllltin FIG.9

J1me 15, 1965 H. ZNAMIROWSKI ETAL 3,189,139

CEILING CONSTRUCTION Filed June 26, 1962 4 Sheets-Sheet 4 FIG. Ill

United States Patent 3,189,139 CEILING CONSTRUCTION Henry Znarnirowski and Martin L. Lydard, Ellicott City,

Md., assignors to Eastern Products Corporation, Baltimore, Md., a corporation of Maryland Filed June 26, 1962, Ser. No. 205,279 11 Claims. (Cl. 189-37) The present invention relates to ceiling constructions and more particularly to suspended ceiling constructions in which a metallic grid system is suspended from primary ceiling members and used to support acoustical tiles or other ceiling panels.

In recent years it has been common in the construction of new buildings and in the renovation of old buildings to employ suspended ceilings in which acoustical tiles or other types of panels are supported by flanged beams, usually made of steel or aluminum. In most such systems the flanged beams are arranged in a rectangular grid system with long parallel beams, called main runners, being joined at suitable intervals by transverse parallel beams called cross Ts. In some systems the bottom flange of the metal beams forms a part of the visible ceiling surface, while in others the metal beams are not visible after the ceiling panels are installed. An example of the former type is the ceiling system shown in United States Patent 2,963,130 to Rosenbaum, which issued December 9, 1960, while an example of the latter type is the ceiling system shown in United States Patent 2,866,233 to Lydard, which issued December 30, 1958.

When the metal beams of a ceiling suspension system are subjected to the high temperatures which accompany fires, the beams tend to twist and buckle and to drop the ceiling panels onto the floor beneath. Such buckling of the beams results from the restraint imposed on expansion of the individual beams by the grid construction and the contact thereof with the walls or other side members of the enclosure. Thus, even though ceiling panels which are highly resistant to fire conditions have been developed, much of the fire retarding advantage of such panels is lost when the panel suspension system buckles and allows some or all of the panels to fall. Falling of the panels may be due to removal of support or to breaking of the panels.

Some grid constructions which will accommodate expansion forces resulting from 'high temperatures have been proposed. A particularly desirable example of such a construction is that described and claimed in the copending patent application of Henry Znamirowski, Serial No. 147,337, filed October 24, 1961. The ceiling construction of said copending application is highly efiicient and relatively simple in design. Nevertheless, for some classes of service an even simpler design which will be more economical to manufacture and install is desirable and the principal object of the present invention has been to provide such a simpler and more economical ceiling construction which will afford satisfactory fire retarding characteristics.

Another object of the invention has been to provide a novel and improved ceiling construction which will resist fire temperatures for prolonged periods of time without buckling in such a way as to break or drop the ceiling panels.

A further object of the invention has been to provide a novel and improved beam which is especially adapted for use in fire retarding ceiling constructions.

Still another object of the invention has been to provide a novel and improved cross T construction which can easily be attached to a main runner and which is specially adapted to accommodate expansion stresses arising from fire conditions.

Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the appended drawings in which:

FIG. 1 is a side elevational view illustrating one form of beam construction in accordance with the invention; FIG. 1A is a side elevational view similar to FIG. 1 and 7 illustrating a modified form of beam construction in accordance with the invention;

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is a bottom plan view of a length of sheet metal illustrating a pre-blanking operation in the formation of the beam of FIG. 1;

FIG. 3A is a bottom plan view similar to FIG. 3 but illustrating a pre-blanking operation in the formation of the beam of FIG. 1A;

FIG. 4 is a side elevational view illustrating one form of cross T in accordance with the invention;

FIG. 5 is a left end elevational view of the cross T of FIG. 4;

FIG. 6 is a right end elevational view of the cross T of FIG. 4;

FIG. 7 is a fragmentary perspective view illustrating assembly of two cross T5 to a main runner in the ceiling construction of the invention;

FIG. 8 is a vertical cross sectional View taken along the line =8!8 of FIG. 9 and showing the cross Ts of FIG. 7 assembled;

FIG. 9 is a horizontal sectional view taken along the line 9-9 of FIG. 8;

FIG. 10 is an enlarged fragmentary view showing one cross T in assembled relation with a main runner;

FIG. 11 is a perspective view of a portion of a suspended ceiling grid system embodying the invention;

FIG. 12 is a fragmentary perspective view of a length of main runner of the type shown in FIG. 1 and illustrating the beam distortion caused by prolonged exposure to fire temperatures;

FIG. 13 is a cross sectional view taken along the line 13-13 of FIG. 12; and v FIG. 14 is a plan view of the beam of FIG. 12.

Referring now to the drawings, and more particularly to FIGS. 1 and 2, there is illustrated a typical suspended ceiling beam 219 embodying the invention. The beam 2% could (be used as either a main runner or cross T, but in the preferred system of the invention the main runners will be formed of beams similar to the beam 20 and the cross Ts will have a different construction to be described below in connection with FIGS. 4-6.

The :beam 20 comprises an upstanding web 21 formed from vertical portions 22 and 23 joined at the top by a rounded or bulbous rib or bulb 24. The web portions 22 and 23 are essentially elongated strips disposed in side by side abutting relationship. Web portions 22 and 23 are provided with outwardly extending flanges 25 and 26, respectively, which form ceiling panel supporting surfaces. As best shown in FIG. 2, the beam in cross section is essentially an inverted T shape. A decorative flange cover 27 caps the flanges 25 and 26 to provide an attractive under surface which is desirable in installations where the under surface of the beam forms a visible part of the installed ceiling. The web portions 22 and 23, the rib or bulb 24 and the flanges 25 and 26 are rolled from a single 7 sheet of metal and are typical of a steel beam construction.

Only a short length of the beam 20 is shown in FIG. 1. In the case of a main runner, the beam 20 might typically be 8 or 12 feet long, while in the case of a cross T or bridging T the beam 26 might typically be two or four feet long. In a grid system such as is shown in the aforementioned Rosenbaum patent, cross TS and main runners have the same general cross-sectional shape but the Patented June 15, 1965 height of the cross TS is considerably less than the height of the main runners.

The web 21 of the beam 24) is provided with an axially (longitudnally) extending cut-out portion 28 which may be termed an expansion relief rout.

The expansion relief r-out 28 is shaped generally as a diamond partially flattened on the lower side and extending from the bottom of web 21 to approximately the middle of the web (designated dimension A in FIG. 1). Typically, for a beam 1 /2" high with a web height of 1 6", dimension A might be 78'. The maximum axial length of rout 28 (dimension B in FIG. 1) is dependent on the coefiicient of expansion of the metal beam, upon the length of the beam and upon the maximum temperature to be accommodated. Typically, for a steel beam expected to be exposed to a maximum temperature of about 2000 F., the dimension B might be 1% for a single rout in a 4' length of beam. The usual 12' beam might have three such routs spaced along the length of the beam. When the actual steel temperature exceeds about 1500 F., the metal becomes somewhat plastic and the compressive stresses which tend to cause buckling are replaced with tension stresses, so that a steel temperature of about 1500 F. will usually represent the maximum temperature which must be accommodated.

In FIG. 3, the beam is shown in developed form, i.e., as a flat sheet of metal, and hence FIG. 3 represents the beam stock before rolling. The lines 29 and 36 represent the locations of the lines of intersection between flange and web section 22 and between flange 26 and web section 23, respectively. The line 31 represents the beam axial center line and the line 32 represents the vertical center line of routs 28A and 2813 which, when the beam is rolled, are in alignment to form rout 28. The routs 28A and 28B are preferably cut out of the beam stock while the same is fiat, i.e., before the stock is subjected to the roll forming operation.

It will be observed that a small triangular portion of blank 28A below line 29 extends into that part of the beam stock which will form flange 25, while a similar portion of blank 23B above line 30 extends into that part of the beam stock which will form flange 26. The lateral extent of these triangular penetrations into the flanges, i.e., the height of the triangles (dimension C in FIG. 3), should be relatively small so as not unduly to weaken the beam. For example, if the flanges are each %3" wide, dimension C might be about The axial length of rout 23 at the lines of juncture of the web and flanges (dimension D in FIG. 1), should be kept relatively small in order to minimize weakening of the beam. In the beam so far described, dimension D typically might be Dimension D should not be less than the maximum beam expansion to be accommodated, and preferably will be slightly greater.

The beam stock, as shown in FIG. 3, is provided with a narrow, elongated, diagonally extending slot 33 which is centered with respect to center lines 31 and 32. Slot 33 is rectangular in shape except for rounded ends and makes a angle with axial center line 31. Typically, slot 33 might be about 1 /8" long (representing a projected length along line 32 of and wide. When the beam is rolled into the shape shown in FIGS. 1 and 2, slot 33 forms an axially extending helical slot in circular rib 24, the ends of the slot extending into the adjacent portions 22 and 23 of web 21. The axial extent of the slot in the rolled beam (dimension E in FIG. 1) is The slot 33, like the routs 28A and 28B, is preferably formed in the beam stock before rolling.

When the beam 20 is subjected to the temperature rise which accompanies fire conditions, the beam will tend to expand in an axial direction. Since the ends of the beam will be restrained against lengthening either by contact with another beam or with a wall, the expansion stresses will have to be accommodated otherwise than by lengthening of the beam in an axial direction.

By reason of the presence of routs 28A and 28B in web walls 22 and 23 and by reason of the presence of slot 33 in rib 24, the expansion stresses in the web 21 will be accommodated by lateral buckling of the web walls 2 2 and 23 in the region above the routs 28A and 28B. This lateral buckling is shown at 22 and 23' in FIGS. 12-14, which illustrate a beam length after exposure to fire conditions. The lateral buckling of the Web walls at 22' and 23' may be in either direction, but preferably will be outward, as shown. There is a tendency, in rolling, for the web walls to separate slightly in the areas above the routs 28A and 28B, and this separation enhances the likelihood of the desired outward buckling. In order to minimize weakening of the beam, it is highly desirable that the centers of the buckled sections be axially separated. By cutting slot 33 at an angle across the beam and extending the slot ends into the web walls 22 and 23, this axial separation will be achieved. Thus the buckling in each web wall will tend to be centered along a line joining the top of the corresponding rout and the point of juncture of slot 33 with the corresponding web wall. Since the slot 33 extends in an axial direction as well as in a direction across the beam, these points of juncture will be axially separated.

Expansion stresses in the rib 24 will be accommodated by opening up of the helix formed by slot 33.

So far as the flanges 25 and 26 are concerned, the expansion stresses will be accommodated by a downward buckling of these flanges in the region of dimension D, i.e., along the lines of juncture of routs 28A and 28B with flanges 25 :and 26, respectively.

Downward buckling of the flanges 25 and 26 in the region of dimension D will not act to drop ceiling panels supported by the flanges 25 and 26 whereas lateral twisting or buckling of these flanges would tend to drop the ceiling panels. By lateral twisting or buckling is meant bending of the flanges 25 and 26 in a plane normal to the plane of web 11. =In the case of an unrelieved beam restrained against elongation, fire temperatures will likely produce twisting or buckling components in both planes. These expansion stresses in an unrelieved beam will produce radical twisting of the beam, resulting in broken ceiling panels which will drop to the floor beneath. But in accordance with the invention expansion stresses in the web are accommodated by the provision of one or more expansion relief routs in the web and a corresponding slot in .the rib and expansion stresses in the flanges are accommodated by producing downward bending of the flanges over a limited length of the beam. The resulting beam distortion will not be such as to cause panels to break and drop or to drop from lack of support.

The absence of the web in contact with the flanges over the dimension D means that the flanges 25 and 26 will n t be so stiff in this region as they will be in the remaining portion of the beam where the presence of the web has a substantial stiffening effect on the flanges. Hence the flanges will be weakest in the dimension D and expansion stresses in the flanges will produce bending in this weakest portion in preference to the stiffer portions. Moreover, provision of tapered web portions 34 and 35 results in a downward component of the horizontal expansion stresses in the web 21 acting to urge flanges 25 and 26 downwardly rather than laterally or upwardly. Upward bending of the flanges might tend to interfere with outward buckling of the web walls and might result in undesirable lateral buckling of the beam as a Whole which-tends to break and drop the ceiling panels.

If the relief rout 28 were rectangular (at least along the lower portion thereof), flanges 25 and 26 would be stiffened because of the presence of the web directly adjacent the portion of the flanges located in the region of the relief rout. Such stiffening would tend to permit appreciable upward or lateral buckling of the flanges as described. The stiffening effect could be reduced by increasing the axial length of the relief rout substantially lbuckling might still occur upwardly as Well as down-.

.wardly.

The triangular extensions of the routs 28A and 28B into the flanges 5 and 26, respectively, as shown in FIG. 3 and also in FIG. 12, assist in causing the flanges to be weakest at a point directly beneath the rout center line and hence these extensions assist in causing the desired downward buckling of the flanges at this point.

FIGS. 1A and 3A illustrate a modified form of beam construction which has certain advantages over that described above, principally as to beam strength both under normal conditions and fire conditions. As shown in FIG. 3A, the expansion relief routs 28A and 28B of FIG. 3 are replaced with differently shaped routs 36A and 36B. Routs 36A and 36B diifer from routs 28A and 233 in that the innermost points or apexes- 37A and 37B are shifted axially away from center line 32 inopposite directions. Typically, each apex might be from center line 32. It is desirable that each apex be located at the same axial position as the comresponding end of slot 33.

Since the dimension A is unchanged and since that portion of each rout outward of .a line 3 8 joining the centers of end curvature of the routs is unchanged, the result is that the legs forming the inner parts of the routs 36A and 36B are of unequal length.

As mentioned above, when the beam is subjected to fire conditions the center of web buckling in each part of the Web will lie along a line joining the apex of the rout and the corresponding end of slot 33. By reason of the shifting of the rout apexes in the construction of FIGS. 1A and 3A, the axial spacing between these centers of web buckling will be even greater than is the case of FIGS. 1 and 3. This results in a beam which is somewhat stronger under normal conditions and substantially stronger under iire conditions than the beam of FIGS. 1 and 3 because the points of minimum strength in each side of the web are axially displaceda substantial distance. In the beam described in connection with FIGS. 1A and 3A this axial displacement typically might be Referring now to FIG. 11, there is shown a portion of a ceiling grid embodying the invention and including portions of three main runners 39, 40 and 41, each of which may be constructed as shown in vFIGS. 1-3. The

main runners will usually be 12' long and the abutting ends may be joined by any suitable splice, for example as shown Iby the splice plate 42 in FIG. 11 joining main runners 39 and 40.

Each main runner is provided along the length thereof with a series of spaced slots for attachment of cross Ts. As shown in FIG. 1, each such slot may be formed in the beam web as an elongated rectangle 43 having an upwardly extending notch 44 in the upper edge thereof and a corresponding downwardly extending notch 4 in the lower edge thereof. A pair of holes 46 and 47 may be provided on each side of each slot 43 to accommodate the wires usually used for suspending the main runners from the ceiling joists or other primary supports. 7

In FIG. 11 two cross T5 48 and 49 are shown spanning the space between main runners 4d and 4-1 Typically, the cross Ts will be 4' long and will be spaced 2' apart. Where it is desired to use smaller ceiling panels, e.g., \2 x 2', it is common to use bridging Ts spanning the space between cross Ts, as shown at 50.

Cross Ts 51 and 52 abut main runner 41 in align ment with cross Ts 48 and 49, respectively. purposes of illustration, cross T 51 is shown spaced away from main runner 40. Another pair of cross Ts 53 and 54 abut main runner 4-1 in alignment with'cross Ts 48 and 49, respectively. It is desirable that the ex pansion relief routs be spaced along each main runner so as generally to equalize the expansion relief action For with respect to the ceiling panels. However, a single expansion relief rout may be provided in each beam, preferably near one end of the beam.

The cross Ts may have expansion relief routs identical in design to those of the main runners. However, in

accordance with a further aspect of the invention, it has been found preferable to use a different form of expansion relief for cross Ts and bridging Ts. Thus, in accordance with this further aspect of the invention, expansion relief for cross and bridging TS is achieved through design of the T ends rather than provision of routs as described in connection with the main runner beams.

Referring now to FIGS. 4-6, there is shown a cross T which has been designated d? to correspond to one of the cross Ts of FIG. 11. The cross T 43 comprises an upstanding web 56 formed from two vertical portions joined at the top by a rounded rib 57. The web por ions are provided with outwardly extending flanges 5d and 59, respectively, which form ceiling panel supporting surfaces. A decorative flange cover 6i caps the flanges 53 and 59.

The opposite ends of the beam 43 are shaped differently. Thus the left end (FIG. 4) has a nose 61 which projects forwardly of the end of the cross T proper, i.e., forwardly of a vertical line 62. The nose 61 is formed as an integral extension of one of the walls forming web 56. The height of nose 61 is approximately equal to the combined height of slot 43 and notches 44 and 45 so that nose 61 may be inserted into this combined opening in a main runner web, as best shown in FIGS. 7l0. To facilitate entry of the nose 51 into the main runner web slot, the outer end is chamfered, as shown at as and 64. end of nose 61 is provided to prevent accidental removal of nose 61 from the main runner slot during the assembly operation, and to prevent the cross T end from working out of the main runner slot under fire conditions. A slot 66 in nose 61 is provided to increase flexibility of the nose.

In assembly, cross T 13 is positioned so that nose.

61 enters slot 43 and the forward ends of flanges 58 and 59 abut against decorative cover 27 along the outer edge of flange 25 of main runner 41.

The inner upper end of nose d1 joins the main body of Web 56 through a shoulder 67. A tongue 68 projects forwardly of shoulder 67 and abuts against the adjacent web of main runner 4-1. The tongue 68 is vertically spaced from the upper edge of nose 61, leaving a recess or slot 69. A recess or slot 7% is formed in the forward end of cross T 48 directly above flange end 48'. The recess 7%) communicates with a larger recess 71 formed between the lower edge of nose 61 and the upper surface of flange 25.

As is best shown in FIG. 10, there is a small vertical displacement between the bottom of main runner 41 and the bottom of cross T 4%. Typically this displacement might be .015".

An axially elongated slot 72 having a vertical for-ward edge 73 and a semi-circular rear edge 74 is provided in the main body of web 56 directly rearwardly of nose 61.

The right end of cross T 48 (FIG. 4) is provided with a forwardly extending nose '75 which has an elongated tongue 76 projecting forwardly therefrom. The nose 75 is joined to the web 56 in a manner similar to that of nose 61, i.e., a shoulder 77 corresponds to shoulder 67, a tongue 73 corresponds to tongue 68, a recess 79 corresponds to recess 69, and a recess 80 corresponds to recess 70. A slot 81 corresponding to slot 66 is provided in nose 75 and a similar slot 8-2 is provided in tongue 76 to facilitate bending of the tongue.

The nose 6 1 and other elements projecting from one end of the cross T are integral with one of the vertical strips forming the web 55, while the nose 75 and other A hook like notch 65 located inwardly of the 4? elements projecting from the other end of the cross T are integral with the other vertical strip forming web 56. Hence two cross Ts reversed end for end, can be axially aligned and their projecting noses can lie in sideby-side abutting contact.

Each cross T has one end (herein called the left end) corresponding to the left end of FIG. 4 and one end (herein called the right end) corresponding to the right end of FIG. 4. As shown in FIG. 7, when the left end of one cross T is inserted into a main runner slot 43, the right end of another cross T is inserted into the same slot from the opposite side of the main runner slot 43. In order to accommodate the tongues 61 and 75, the width (axial length) of the notches 44 and 45 should be slightly greater than the combined thickness of tongues 61 and 75 so that the notches will readily accept the tongues. As best shown in FIG. 10, the height of slots 43 including notches 44 and 45 should be somewhat greater than the heights of cross T noses 61 and 75; typically this greater height might be When the cross Ts are positioned as shown in FIGS. 8 and 9, the ends of the cross T flanges abut against the respective main runner flanges and the tongues 68 and 78 abut against respective faces of the main runner web. The cross Ts are then locked in place by bending the tongue 76 through the slot 72 until the forward part of tongue 76 lies against the opposite face of nose 61. As best shown in FIG. 8, the tongue 76 is bent along a vertical line running through slot 82, the presence of which facilitates the bending.

Typically, for a 4' cross T the tongues 68 and 78 might be A long and Ms high, the slots 6? and 79 might be A long and ,4 hight and the slots 78 and 80 might be A" long and high.

When subjected to the elevated temperatures which accompany a fire, the cross Ts will be subjected to axial expansion stresses but will be restrained against expansion by reason of abutting against main runners at each end thereof. For example, in FIG. 11 the cross T5 48 and 49 will be restrained against axial expansion by main runners and 41. In accordance with the invention, the axial expansion stresses are accommodated without twisting or buckling of the cross T by means of the cross T end configuration.

Referring to FIG. 10, as the cross T 48 becomes subjected to substantial expansion stresses, the tongue 68 will crumple and the cross T flange end 48' will bend upwardly into the space for-med by the slot and extend into the space 71 between the main runner flange top surface and the bottom of nose 61. The action of the right end of the beam will be same with the tongue 78 crumpling and the right end cross T flange bending upwardly and entering the space between the main runner flange top surface and the nose 75. Upward bending of the cross T flange is facilitated by the excess height of slots 43 with respect to noses 61 and since the clearance thus afforded allows the whole cross T end to move up. It will sometimes happen that the cross T ends will be bent downwardly and hence ride under rather than over the main runner flanges. This might be due, for example, to the presence of a light fixture supported by the grid system. Upward bending is preferred, but the downward bending can be accommodated.

The fact that the bottom surface of the cross T is slightly higher than the bottom of the main runner (a height differential of .015 having been suggested as typical hereinbefore) is important in insuring that the ends of the cross T flanges bend upwardly, as described, into the spaces provided to accommodate them. If the cross T flanges did not move as described, axial expansion thereof would result in serious distortion of these flanges and the main runner flanges against which they abut. Depending upon the way in which the bending occurs, the cross T flanges may crurnple shoulders 83 and 84 between the top of slot 70 and the bottom of nose 61 and between the top of slot and the bottom of nose 75, respectively.

In effect, the cross T will ride up onto the main runner flanges to accommodate the expansion stresses, and this is accomplished with crumpling or distortion of cross T parts which will not produce overall buckling of either the cross T or main runners and hence will not act to drop or break ceiling panels. As is best shown in FIGS.

8 and 9, as the end 48' of a cross T rides up onto the adjacent main runner flange, the slot 72 will accommodate tongue 76 so that this tongue will not inhibit cross T expansion.

Bridging Ts may be constructed in the same manner as cross Ts and will preferably have expansion stresses relieved in the same way. Hence a bridging T such as shown at 50 in FIG. 11 will bear the same relationship to cross Ts 48 and 49 as the cross T 48. bears to main runners 40 and 41.

While the invention has been described in connection with specific embodiments thereof and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A beam for use in a fire retarding structural ceiling system, comprising a pair of elongated metal strips disposed in side by side relationship and forming an upstanding web, an elongated bulbous n'b joining the tops of said strips, and an elongated flange extending laterally from each side of the base of said web whereby said beam has substantially an inverted T cross section, each of said strips having an opening extending upwardly from the base thereof at an intermediate location in the length of said beam, said openings being in substantial axial alignment, said openings forming an expansion relief space in a lower portion of said web, said rib having an elongated slot extending in a spiral path from one side of said web to the other side of said web and being in substantial axial alignment with said space whereby when said beam is subjected to expansion stresses accompanying fire conditions said strips will buckle laterally in the region above said openings and said flanges will buckle downwardly in the region below said openings thereby to relieve said expansion stresses without substantial twisting of said beam.

2. A beam for use in a fire retarding structural ceiling system, comprising a pair of elongated metal strips disposed in side by side relationship and forming an upstanding web, an elongated bulbous rib joining the tops of said strips, and an elongated flange extending laterally from each side of the base of web whereby said beam has substantially an inverted T cross section, each of said strips having an opening extending upwardly from the base thereof at an intermediate location in the length of said beam, said openings being in substantial axial alignment, said openings forming an expansion relief space in a lower portion of said web, said rib having an axially and laterally extending elongated slot in substantial axial alignment with said space and extending in an arcuate path from one side of said web to the other side of said web whereby when said beam is subjected to expansion stresses accompanying fire conditions said strips will buckle laterally in the region above said openings and said flanges will buckle downwardly in the region below said openings thereby to relieve said expansion stresses without substantial twisting of said beam.

13. A beam for use in a fire retarding structural ceiling system, comprising a pair of elongated metal strips disposed in side by said abutting relationship and forming an upstanding web, an elongated bulbous rib joining the tops of said strips, and an elongated flange extending laterally from each side of the base of said web and each being integral with a respective one of said strips whereby said beam has substantially an inverted T cross section, each of said strips having an opening extending upwardly from the base thereof at an intermediate location in the length of said beam, said openings being in substantial axial alignment and each having a generally diamond shape with a flattened bottom at the level of said flanges, said openings forming an expansion relief space in a lower :portion of said Web, said rib having an axially and laterally extending elongated helical slot in substantial axial alignment with said space whereby when said beam is subjected to expansion stresses accompanying fire conditions said strips will buckle laterally in the region above said openings and said flanges will buckle downwardly in the region below said openings thereby to relieve said expansion stresses without substantial twisting of said beam.

4. A beam as set forth in claim 3 in which the apex of each of said openings is located approximately at the midpoint of the height of said web.

5. A beam as set forth in claim 3 in which the apex of each or" said openings is located in substantial axial alignment with the axial midpoint of said slot.

6. A beam as set forth in claim 3 in which the apexes of said openings are each located in substantial axial alignment with the point of juncture of said slot with the corresponding strip.

7. A beam as set forth in claim 3 in which said slot extends into a respective oneof said strips at each end thereof.

8. A beam for use in a fire retarding structural ceiling system, comprising a pair of elongated metal strips disposed in side by side abutting relationship and forming an upstanding web, an elongated bulbous rib joining the tops of said strips, and an elongated flange extending laterally from each side of the base of said web and each being integral with a respective one of said strips whereby said beam has substantially an inverted T cross section, each of said strips having an opening extending upwardly from the base thereof at an intermediate location in the length of said beam, said openings being in substantial axial alignment and each having a substantial axial extent along the line of juncture of the corresponding strip and flange, the edge of each opening in the region adjacent said line of juncture being angularly disposed with respect to the plane of said flanges so that the areas of said strips in the regions adjacent said openings and near said lines of juncture are tapered, said openings forming an expansion relief space in a lower portion of said web and each having upper edges converging at an apex, said rib having an axially and laterally extending elongated helical slot in substantial axial alignment with said space and extending partially into each strip at the ends thereof whereby when said beam is subjected to expansion stresses accompanying .fire conditions said strips will buckle laterally in the region above said openings and said flanges will buckle downwardly in the region below said openings References Cited by the Examiner UNITED STATES PATENTS 2,689,630 *9/54 Drury 189-85 2,829,743 4/ 5-8 Strauss et a1. 189-85 X 3,142,867 7/ 64 Brown et al 18936 RICHARD W. COOKE, 111., Primary Examiner. 

1. A BEAM FOR USE IN A FIRE RETARDING STRUCTURAL CEILING SYSTEM COMPRISING A PAIR OF ELONGATED METAL STRIPS DISPOSED IN SIDE BY SIDE RELATIONSHIP AND FORMING AN UPSTANDING WEB, AN ELONGATED BULBOUS RIB JOINING THE TOPS OF SAID STRIPS, AND AN ELONGATED FLANGE EXTENDING LATERALLY FROM EACH SIDE OF THE BASE OF SAID WEB WHEREBY SAID BEAM HAS SUBSTANTIALLY AN INVERTED T CROSS SECTION, EACH OF SAID STRIPS HAVING AN OPENING EXTENDING UPWARDLY FROM THE BASE THEREOF AT AN INTERMEDIATE LOCATION IN THE LENGTH OF SAID BEAM, SAID OPENINGS BEING IN SUBSTANTIAL AXIAL ALIGNMENT, SAID OPENINGS FORMING AN EXPANSION RELIEF SPACE IN A LOWER PORTION OF SAID WEB, SAID RIB HAVING AN ELONGATED SLOT EXTENDING IN A SPERIAL PATH FROM ONE SIDE OF SAID WEB TO THE OTHER SIDE OF SAID WEB AND BEING IN SUBSTANTIAL AXIAL ALIGNMENT WITH SAID SPACE WHEREBY WHEN SAID BEAM IS SUBJECTED TO EXPANSION STRESSES ACCOMPANYING FIRE CONDITIONS SAID STRIPS WILL BUCKLE LATERALLY IN THE REGION ABOVE SAID OPENINGS AND SAID FLANGES WILL BUCKLE DOWNWARDLY IN THE REGION BELOW SAID OPENINGS THEREBY TO RELIEVE SAID EXPANSION STRESSES WITHOUT SUBSTANTIAL TWISTING OF SAID BEAM. 